Antennas are widely used in many Radio Frequency (RF) communications systems. A typical directional antenna may include a parabolic reflector, and a feed horn positioned at the focus of the reflector. A waveguide is connected between the processing electronics, that is, receiver or transmitter, and the feed horn. Accordingly, RF signals may be received and/or transmitted.
Another type of common antenna is the phased array antenna which includes a pattern or array of conductive elements, for example. The antenna elements are typically mounted on a planar substrate and supplied with RF energy at different respective phase relationships, such as to provide beam steering without moving the antenna structure. Forming or assembling the conductive elements on a rigid planar substrate is relatively easy.
Yet another type of antenna may desirably have a three-dimensional pattern of conductive elements for more complex beam steering or to handle various polarizations of RF signals. Unfortunately, conventional manufacturing techniques for accurately and efficiently producing such an antenna with a complex pattern of conductive elements have been unsuitable.
Relating to manufacturing of a basic reflector antenna as discussed above, U.S. Pat. No. 3,536,800 to Hubbard discloses a molding process for making radio frequency devices including the reflector antenna, a feed horn and a waveguide, or other RF device having a highly complex conducting surface. A rigid mold is initially constructed to have an outer surface which has the exact contour desired for the RF conducting surface. A parting agent coating is preferably applied over the outer mold surface. A film of metal is formed over the parting agent by spraying fine particles of molten metal onto the outer surface until the metal has a sufficient thickness. The outer face of the metal film is coarse and porous and a layer of plastic is applied onto the outer face and forms a bond therewith. The plastic layer and metal layer are removed from the mold. No additional shaping or forming of the RF conducting surface is necessary.
Unfortunately, the approach described in the Hubbard patent is fairly limited to coating the entire surface with a metal layer, especially where a complex pattern of conductors is required as disclosed, for example, in U.S. Pat. No. 4,792,808 to Hildebrand. This patent is assigned to the assignee of the present invention, and discloses an array of antenna elements distributed over half of an ellipsoid, that is, a geometrical surface defined by half an ellipse of revolution. The antenna may be used for providing complete hemispherical coverage as attractive for airborne communication, and does so with fewer elements and effectively uniform gain as compared with conventional spherical dome or tetrahedral configurations.
It is especially difficult to form an antenna with a spherical portion and a complex pattern of conductors on the interior of the spherical portion as may be desirable in certain applications. The difficulties are further compounded when the radius of curvature for such an antenna are relatively small, such as on the order of a few inches.